#include <iostream>
#include <cstring>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
    int x1,y1,x2,y2;
    cin >> x1 >> y1 >> x2 >> y2;
    if(abs(x1-x2)>=abs(y1-y2)) cout << abs(x1-x2);
    else cout << abs(y1-y2);
    return 0;
}